The last three values are those obtained by extrapolation with platinum-rhodium and platinum-iridium couples.

Abolish, now, one of the percipients, and the interpolation changes into 'extrapolation.'

Word Origin and History for extrapolation

n.

by 1867, from extra- + back half of interpolation; original sense was "insert intermediate terms in a mathematical series." Transferred sense of "drawing a conclusion about the future based on present tendencies" is from 1889. Cf. extrapolate.

extrapolation

[(ik-strap-uh-lay-shuhn)]

A mathematical procedure designed to enable one to estimate unknown values of a parameter from known values. A common method of extrapolation is to look at data on a curve, then extend the curve into regions for which there is no data. Extrapolation is often used to predict the future.